Bitcoin (or any deflationary asset) can never be a "currency"...

A currency must be very slightly inflationary to encourage investment & exchanging for goods & services. This encourages a very liquid and active and growing economy.

A deflationary currency discourages purchasing & investment. This leads to a stagnant and desperate economy.

For example: a gallon of milk costs $3. Last year it cost $3. Maybe 10 years ago it cost $2.50 and maybe 20 years ago it cost $1, but day to day, the price of milk is the same in USD.

If a grocery store sold items priced by BTC, they would need a minute-by-minute price tracker because of the volitility.

The USA tries (with a big "haha!" and a huge "kinda, with caveats") to print currency at a 1-4% inflationary growth compared to the overall economic growth.

But you say: "Someday, bitcoin will become more stable?" Stable to what? The economy grows. Bitcoin is stuck at 21m coins. That means it is deflationary. If bitcoin was a currency, as the economy grows, bitcoin must in relation gain more economic value. So it is wiser to not spend your bitcoin today because you'll get more milk for the same price tomorrow. It is wiser to not invest in anything but a sure thing because you are already growing your assets just by holding on to them.

This creates an incentive to not invest or spend. This creates a stagnant economy.

Think of your salary or wages? How do you track that and adjust that day to day or month to month in relation to the overall economy? Maybe according to GDP or some other total market growth indicator? Well guess what? We've got one. It's called "the dollar."

Bitcoin can never be a universal currency as it is programmed today. Impossible, will never happen.